Cable television systems presently distribute signals to millions of television receivers in homes throughout the country over a distribution network of copper conductor coaxial cable. Although the quality of the signals provided each subscriber is generally better than could be achieved using an antenna system at each receiver site, the coaxial cable distribution system suffers from bandwidth limitations and noise problems that are inherent to coaxial conductors and to the amplifiers used with them.
A substantial improvement in the quality of the signals distributed might be obtained by using optical fibers to distribute the television signals either in analog form, or as the technology develops and digital TV receivers become commonly available, in digital form. However, the cost of implementing an optical fiber distribution system linking individual television receivbers to a central source station has previously been considered prohibitive. If each customer were linked to the central station by a single optical fiber for each channel, the size of the distribution cables, the labor cost to install the system and the number of splices required would be enormous. Clearly, such a system is not practical nor cost effective.
An alternate approach would be to distribute each of the video signals over an optical fiber from a source station to each of a plurality of distribution centers, and then to distribute the signals to each receiver connected to the distribution centers by separate distribution optical fibers. As is customary in existing cable systems using coaxial cables, a basic service could be provided to each customer, with additional stations or services being made available to the customer at an added cost. Although scrambler technology could be used to encode extra cost programming, it would be preferable to transmit each extra cost channel separately to the distribution centers, and then distribute them to specific subscribers who have paid for the option. The optical fiber distribution system should thus be able to selectively connect a specific subscriber to a particular signal propagated to the distribution center from the central station.
In addition, it would be desirable for the optical fiber distribution system to support bidirectional communication between the receivers and the central station, thereby enabling customers to select specific extra cost programming, participate interactively in surveys, order merchandise marketed on a video channel, etc. Coaxial cable systems are presently incapable of supporting bidirectional communications, except on a very limited basis.
To effectively implement the above-described fiber optic distribution system, a device is required that is capable of replicating a light wave signal for distribution to a plurality of receivers. The prior art includes beam splitters for dividing an input signal between two fiber optic cables, but this would not provide an acceptable solution where the same light wave signal must be distributed to several hundred subscribers, nor would it sufficie for bidirectional communications.